In recent years, substantial research interest has been directed toward nano scale structures due to the unique properties that are observed at the nanoscale. Common nanoscale structures include nanoparticles, nanowires, and nanotubes, for example. Metallic nanowires, particularly copper nanowires, for example, have drawn considerable interest for their potential use in nanoelectrical and nanomechanical devices due to the high thermal and electrical conductivity of bulk copper.
Methods for synthesizing nanoscale structures can be divided into template-assisted methods and template-free methods. Illustrative template-free methods include chemical vapor deposition, vapor-solid reaction growth, solid-phase electrochemical deposition, physical vapor vacuum deposition, irradiation methods, thermal-assisted photoreduction methods and liquid-phase reduction methods. All but the liquid-phase reduction methods, including hydrothermal and solvothermal syntheses, typically produce polycrystalline material. In contrast, liquid-phase reduction methods can, under suitable conditions, produce single-crystalline nanowires having high aspect ratios in good yield.
Although the aforementioned nanoscale structures have been the subject of a majority of current research activities, other nanoscale structures also remain of considerable interest. Nanorings or nanobelts, in particular, are an especially intriguing nanoscale material having a closed loop structure that may be of potential commercial relevance. Such nanorings may have special properties, including novel optical and magnetic properties, that are not duplicated by the bulk materials themselves. Further, since the nanorings have a closed loop structure, the interior portion of the nanorings may be used to contain molecules in a semi-isolated environment. Although nanorings are a nanoscale structure of considerable interest, their synthesis remains very difficult. Synthesis of single-crystalline nanorings is an especially daunting task. In one of the very few successful efforts at synthesizing single-crystalline nanorings, ZnO nanorings have been prepared by a high temperature vapor deposition process. Metallic gold and silver nanoring structures are also known, albeit in polycrystalline form. Single-crystalline metal nanoring structures are presently unknown.
In view of the foregoing, efficient methods to prepare metal nanorings, particularly single-crystalline metal nanorings, would be of considerable benefit in the art. Facile syntheses of single-crystalline metal nanorings would further expand the realm of potential commercial applications for these nanomaterials.